It has been found that animals that are maintained in a building where the air has high airborne particulate or aerosol concentrations are less productive. By less productive, it is meant that the animals gain weight at a rate that is slower than the rate at which animals that are maintained in a building that does not have a high airborne particulate or aerosol concentration.
Additionally, animals that are maintained in a building where the air has a high airborne particulate or aerosol concentration have a higher mortality rate than similar animals that are maintained in a building that does not have a high airborne particulate or aerosol concentration.
Airborne pathogens are a significant issue in commercial pig facilities. Most of these pathogens are attracted to an airborne particle or aerosol and travel through the air. Collectively these diseases cause tremendous reductions in productivity. When airborne particles or aerosols are removed from the air, many pathogens are removed from the air as well. Cleaner air results in fewer challenges to the animals' respiratory and immune response systems.
The porcine reproductive and respiratory system virus (PRRSv), for example, has an affinity for macrophages found in the lungs of pigs. In contrast to the typical functions of macrophages to ingest and remove invading bacteria and viruses, the porcine reproductive and respiratory syndrome virus multiplies within the macrophages until the concentration of the viruses is sufficiently large that the virus kills the macrophages.
The destruction of the macrophages in the animal leaves the animal vulnerable to attack by bacteria and other viruses, which can decrease the animal's growth rate and potentially lead to the death of the animal. The extent of such effects is impacted by the overall health of the animal and the other animals in the herd.
In addition to the preceding symptoms of porcine reproductive and respiratory syndrome, piglets that are born to sows that have this virus have decreased birth weight and are less viable than piglets born to sows that do not have this virus.
A common way for the porcine reproductive and respiratory syndrome virus to be transmitted is through the air. A technique that has previously been used to trap this virus is to pass air in the building in which the pigs are raised through a fine filter. There are challenges associated with using the filter systems to trap viruses.
The air circulation system needs to move a large volume of air to provide continuous fresh air for the animals. Dust and other air contaminants are trapped in these costly filter systems. There are significant expenses associated with the filters that are capable of trapping significant percentages of the viruses.
Poultry production includes two major categories—meat production and egg production. Currently, most poultry produced in North America is grown under close control on highly specialized farms. The evolution from small flocks to large commercial units after World War II was facilitated by advances in the knowledge of nutrition, breeding, housing, disease control, processing of poultry and eggs, and by improvements in transportation and refrigeration that made possible distant marketing of fresh products.
Poultry produced for meat production is commonly referred to as broilers. During the last few decades, broiler production has greatly increased as a result of Americans becoming more health conscious, as poultry is viewed by certain persons as healthier than other meats that are typically consumed by humans. The increased broiler production also resulted from the increased demand for export of poultry products to other countries.
The facilities that are typically used in conjunction with commercial poultry production each contain a relatively large number of birds. For example, each poultry production facility may house more than 20,000 birds.
The poultry production facilities confine the birds to protect them from predators and environmental extremes that would cause mortality or reduce growth, feed efficiency, immunocompetence, fertility or egg production. The poultry production facilities thereby facilitate efficiently managing a large volume of birds.
While the poultry production facilities enable a large volume of birds to be simultaneously raised, the large volume of birds generate waste materials that must be dealt with. One such waste material is airborne dust and biological particles.
Electrostatic precipitation of dust has been historically used to control emission from industrial smokestacks. This technique has also been used to remove dust from the air inside a living space.
When using electrostatic precipitation, ions are placed into the air space that is to be treated to polarize any particles in the air. Thereafter, the polarized particles are removed from the air by attraction to a grounded collection plate.
Over time, a progressively thick layer of particles collect on the collection plate. This progressively thicker layer of particles reduces the efficiency of the electrostatic precipitation system because the layer of particles insulates the collection plate from the polarized airborne particles. To enhance the efficiency of the electrostatic precipitation system, it is necessary to periodically clean the collection plates to dislodge the accumulated particles.
Disadvantages of these types of electrostatic precipitation systems are that only a limited airspace may be treated by one collection plate. The cost and size of multiple collection plate systems reduces the feasibility of using electrostatic particle ionization in very dusty and larger air spaces.
Mitchell et al., U.S. Pat. No. 6,126,722, uses corona points to discharge negative ions into a large air space that is being treated. This system relies on grounded surfaces inside and confining the air space to attract and hold the ionized particles.
While this system is effective at economically treating a large, dusty air space to reduce dust in the air, the polarized particles accumulate on the grounded surfaces and cause the grounded surfaces to become progressively more insulated. This process decreases the efficiency of this system.
Even though manual and/or mechanical cleaning will maintain the desired ionization level, the cost and limited ability to manually or mechanically clean grounded surfaces makes such a system a less than optimal result.